In a brake device for a vehicle, a hydraulic pressure control device is used for a device which controls a valve portion (for example, an electromagnetic valve) so that the hydraulic pressure (actual hydraulic pressure) in the hydraulic pressure chamber associated with the braking force approximates the target hydraulic pressure which is set in response to the braking operation by a driver of the vehicle. According to a generally used hydraulic pressure control device, a feed-back control is adopted which controls the flow-rate of the valve portion based on the difference between the actual hydraulic pressure and the target hydraulic pressure. In such feed-back control, a control constant is set for restricting the fluid amount (fluid inflow or fluid outflow amount) flowing into or out of the hydraulic pressure chamber. The control constant is normally set to the maximum value that can assure the control stability. Such hydraulic pressure control of the brake device for a vehicle is shown in, for example, a patent publication No. JP 2002-316631A.